1. Field of the Invention
The invention relates to a negative reference voltage generating circuit that is, for example, used in a NOR type flash memory and generates a negative reference voltage, and a negative reference voltage generating system using the negative reference voltage generating circuit.
2. Description of Related Art
FIG. 7A and FIG. 7B are vertical cross-sectional views of a NOR type flash memory cell of Conventional Example 1, which show the voltage relationship required for performing Fowler-Nordheim programming/erasing operations at the maximum voltage of 18V or 10V. In FIG. 7A and FIG. 7B, 100 represents a semiconductor substrate, 101 represents a control gate, 102 represents a source, 103 represents a drain, and 104 represents a floating gate.
For example, a NOR type flash memory requires high speed performance during random access, and as shown in FIG. 7A and FIG. 7B, for the programming/erasing operations, a positive intermediate voltage, such as 10V, and a negative intermediate voltage, such as −8V, are used in place of a positive high voltage. By using the positive intermediate voltage and the negative intermediate voltage, the metal-oxide-semiconductor (MOS) transistor used in the peripheral circuit exhibits better performance than a high voltage transistor. It is because that a thin gate oxide film and a short gate length can be used.
In order to generate the positive voltage, generally a bandgap reference (BGR) voltage generating circuit is used, for example, in the peripheral circuit of a NAND type flash memory.